Siberian Branch of RAS, (Russia)

Transcription

1 MECHANOCOMPOSITES ON THE BASIS OF SEVILEN N.Z. Lyakhov 1, I.A., Vorsina 1, T.F. Grigorieva 1, T.A. Udalova 1, S.V. Vosmerikov 1, E.V. Ovchinnikov 2, V.A. Struk 2 1 Institute of Solid State Chemistry and Mechanochemistry, Siberian Branch of RAS, (Russia) grig@solid.nsc.ru 2 Yanka Kupala Grodno State University, Grodno (Belarus) ABSTRACT Mechanocomposite 2) and kaolinite obtained through joint mechanical activation, were studied by means of IR spectroscopy and X-ray phase analysis. It was established that mechanical activation of mixtures, depending on the percentage of component content in the initial mixture, results in the formation of mechanocomposites in which the polymer and silicate are bound with a chemical bond. This bonding may occur through water bridges. INTRODUCTION Synthetic high-molecular compounds, or polymers, become perfectly irreplaceable construction and anti-corrosive materials due to the principal possibility to combine any desirable properties in one substance because of the introduction of different modifying agents [1], and at present they are winning increasingly broad application in technology and in everyday life replacing traditional materials. Most frequently used modifying agents are kaolinite, talc, pyrophyllite, mica, glass, carbon fiber, metal oxides and hydroxides, aerosil (nanometer-sized SiO 2, d 10 nm) etc. [1]. The choice of modifying agent depends on under which conditions the polymer composite is used. It is also necessary to take into account the fact that the basic characteristics of the composite depend not only on the nature of the chosen modifying agent and its percentage in the composite but also on the character of bonding between the polymer and the modifying agent because adhesion of the polymer to the particles of the modifying agent occurs during composite preparation independently of the method used to obtain it. As a result, physical and chemical bonds between them are formed; they depend on the nature of both the polymer and the modifying agent. Sevilen, ethylene vinyl acetate, is a co-polymer of ethylene and vinyl acetate, one of the most relevant polymers; it possesses with increased adhesion to different materials, and its properties depend mainly on vinyl acetate content (5-30% mass). Sevilen is well compatible with various modifying agents, which ensures broad application of composites based on it. Due to its valuable characteristics, Sevilen is used in electronics and in radio industry, for insulation of high-frequency cables in radar, television and telemechanic systems. Wollastonite in polymeric compositions based on Sevilen, renders higher thermal stability and durability of the polymer, the stability of size and mechanical characteristics of products made of these composites [2]. A new class of radiation cross-linked composites was developed on the basis of Sevilen and aluminum hydroxide for the production of thermally shrinkage elements of cable adapters [3]. Aluminum hydroxide in these composites decomposes to form aluminum oxide when heated above 220º C releasing water and absorbing heat. Because of this, it is used as a flame retardant for polymers. The physicomechanical characteristics of the composites of Sevilen with mineral substances are not worse than those of the initial polymer but even surpass some of its parameters; what is of importance, the cost of the composites is lower [3]. 42

2 In order to understand the general situation with the effect of introducing of a specific modifying agent into a polymer, it is necessary to evaluate the physicomechanical properties, the cost of thus developed polymeric composite, and the mechanochemical interactions between the polymer and the modifying agent: what kinds of bonds are formed during the formation of the composite, how these bonds can change depending on the content of the modifying agent in the composite. The goal of the present work was to obtain polymeric composites formed on the basis of Sevilen with aerosil and kaolinite as modifying agents, and to investigate the character of bonding in these composites. Materials and methods of investigation We used Sevilen 113 as the polymer, and modifying agents were non-calcined nanometer-sized aerosil SiO 2 (d 10 nm) and kaolinite. Aerosil is one of the promising materials to form composite structures of inorganic or organic nature, including various polymers. Attention to aerosil is connected with the fact that it is structurally active, similarly to all other ultrafine materials, and possesses well developed surface. Kaolinite as a modifying agent possesses an optimal lamellar particle shape. Mechanical activation was carried out in AGO-2 bal mill with water cooling. The IR absorption spectra were recorded using the Tensor-27 and Specord-75 IR instruments. The samples were prepared for recording using a standard procedure. The X-ray phase analysis (XPA) was performed with D-8 Advance Bruker diffractometer (CuК radiation). RESULTS AND DISCUSSION Sevilen 113 is a copolymer of ethylene with vinyl acetate; its structural formula is - [-CH 2 -CH 2 -] n -[-CH 2 -C-O-CO-CH 3 -] m -. The IR spectra and X-ray diffraction patterns of the polymer are presented in Figure 1, with the assignment of the characteristic bands of the polymer. The IR spectrum and X-ray diffraction patterns of the polymer remain almost the same after activation. Because of this, it may be accepted that the structure of Sevilen after activation remains unchanged, the polymer gets dispersed. The authors of [4] studied the acidic and basic prperties of inorganic powders and established that some amount of acid centers and a small number of basic ones are formed on the surface of both kaolinite and SiO 2. We demonstrated [5] that the joint mechanochemical activation of aerosil (SiO 2 ) with organic acids involves mechanochemical reaction in which silicon dioxide interacts with monomer acid molecules through adsorbed water of aerosil. Water molecules form relatively strong hydrogen bonds with basic active centers on silicate surface and with hydroxyl groups of monomer acids: aerosil adsorbed water acid. In the case of hydroxy- and amino acids, both basic and surface centers of aerosil participate in the interaction. During the joint mechanical activation of kaolinite with organic acids [6] mechanochemical neutralization takes place: the basic active centers of kaolinite interact with acidic centers of organic acids. As a result, the salts of organic acids with kaolinite are formed. Sevilen + aerosil The mechanochemical interaction of Sevilen with aerosil during their joint mechanical activation proceeds very actively. One can see in Figure 1 (Sevilen content in mix- 43

3 ture: 20 % mass) that in 10 s after the start of activation the IR spectrum of the mixture shows that the second maximum at 1705 cm -1 attributed to the vibrations of the bond carbonyl groups of the polymer, ν b. С=О, appears at the band ν С=О with the maximum at 1745 cm -1 (Figure 1, curves 2, 3). Figure 1 IR absorption spectra for Sevilen 113 before mechanical activation (1), for the mixtures with aerosil before (2) and after activation 10s. (3), 4 min (4, 5). Sevilen content in mixture: 20% (mass.) (2-4), 30% (mass.) (5). At the same time, we observe a shift of the ν 3 (SiO 4 - ) band of aerosil, clear broadening of all its bands, the appearance of absorption bands of water: ρ Н 2 О, cm -1, and ν ОН in the region cm -1. With an increase in activation time to 4 min, the intensities of ν b. С=О, ν, ρ Н 2 О bands increase (Figure 1, curve 4). The X-ray diffraction patterns of the initial mixture of Sevilen with aerosil (Figure 2, curves 2, 4) exhibit a halo belonging to aerosil, in the angle region 2 θ = 15-35º with Sevilen reflection at d = 4,205. After activation for 10s, the reflection shifts to larger angles; after 4min it becomes almost imperceptible. These results allow us to assume that, similarly to the case of the joint activation of poly-n-vinylpyrrolidone with aerosil [7], the joint mechanical activation of Sevilen with aerosil involves the mechanochemical interaction of the polymer with the silicate, with the formation of a composite in which the components are bound with each other through bridges composed of the adsorption water of aerosil. 44

4 Figure 2 X-ray diffractograms for Sevilen 113 before mechanical activation (1), for the mixtures with aerosil before (2) and after activation 10s. (3), 4 min (4, 5). Sevilen content in mixture: 20% (mass.) (2-4), 30% (mass.) (5). The formation of similar composites was observed by the authors of [8] when studing the adsorption of organic substances by layered silicates. Water molecules in these composites form hydrogen bonds with basic centers on aerosil surface and with active oxygen atoms of Sevilen: Sevilen adsorbed water aerosil. Different versions of such bridges that can exist at the same time are possible [8]. An increase in activation time causes gradual amorphization of the composite. The presence of the band related to unbound carbonyl groups ν С=О 1745 cm -1 in the IR spectra of the sample activated for 4 min (Figure 1, curves 4, 5) provides evidence that the mechanochemical interaction between the components in the mixture did not proceed till completeness. An increase in polymer content in the mixture to 30% mass (Figure 1, curve 5) causes an increase in the intensity of the maximum corresponding to the vibrations of free carbonyl groups. This is due to the fact that the number of basic active centers formed during mechanical activation on the surface of silicon dioxide is not large [4]. It may be assumed that the number of chemically unbound carbonyl groups will be smaller in the composite with polymer content < 20% (mass). Sevilen+kaolinite Unlike for the mixtures with aerosil, mechanochemical interaction of the components is observed in the mixture with kaolinite only after activation of the mixture for 4 min, independently of the percentage of Sevilen in it (Figure 3, curves 1, 3, 6). 45

5 Figure 3 IR absorption spectra of the mixtures sevilen 113 with kaolinite before (1, 5) and aftermecanical activation 1 min (2), 4 min (3, 6), 10 min (4). Sevilen content in mixture: 10% (mass.) (1-4), 20% (mass.) (5, 6). This is evidenced by the IR spectra of the mixtures activated for 4 min: the second maximum appears at the band of the stretching vibrations of carbonyl groups ν С=О, 1745 cm -1, ν b С=О 1700 cm -1. With an increase in activation time, the intensity of the maximum of ν b С=О band increases gradually. After activation of the mixture for 10 min, the intensities of these two maxima turn out to be equal (Figure 3, curve 4). At the same time, the IR spectra exhibit a decrease in the intensities of the bands of antisymmetric ν as and symmetric ν s Si-O-Si stretching vibrations of the tetrahedrons of silicon oxygen framework, in the region of and cm -1. The intensities of the bands related to the stretching and bending vibrations of hydroxy groups of kaolinite, ν, δ cm -1 and cm -1, respectively, somewhat decrease. However, the parameters of vibrational bands ν, δ of Si-O - bonds, corresponding to the region cm -1 and the bands with the maxima at 465, 425 cm -1 (Figure 3, curves 2, 4, 6) do not exhibit any noticeable changes. According to the XPA data (Figure 4, curves 1-6), the destruction of kaolinite structure in the presence of the polymer proceeds slower. 46

6 Figure 4 Diffractograms of the mixtures sevilen 113 with kaolinite before (1, 5) and aftermecanical activation 1 min (2), 4 min (3, 6), 10 min (4). Sevilen content in mixture: 10% (mass.) (1-4), 20% (mass.) (5, 6). All the major reflections of kaolinite are observed in the diffraction patterns, only their intensity decreased; the reflections broaden. Nevertheless, the obtained data allow us to assume that the mechanochemical interaction of Sevilen with kaolinite proceeds during the joint mechanical activation due to active centers formed on the surface of the silicate and the polymer. CONCLUSION Thus, investigation showed that in the case of polymer content 20% (mass) in the mixture with silicates, mechanochemical interaction of the components takes place; during this process, the active centers of the basic character in the polymer interact with the active centers of the silicate; the result is the formation of mechanocomposite. In the case of the mixtures of polymer with aerosil, this interaction proceeds through water bridges. ACKNOWLEDGTMENT The work is carried out under the Integration Project of SB RAS No. 19 and BRFFI No.X12CO

7 References 1. Filler for polymeric composition materials: reference book by edited Babaevskogo P.G. Moscow. Chemistry Suhinina A.V. Working up of thermally shrinkage filler for polymeric composition materials on the base of sevilen for of cable adapters. Author s abstract prepared by candidate of technical sciences. Moscow Osypchike V. S., Suhinina A.V., Gureev Yu.A. Investigation of thermally shrinkage electrical insulating tape on the base of sevilen and mineral filler for production factory -made good cable. Plastic mass Magazine 2008 (6) Ikekava A., Hayakawa S., Mechanochemistry of organic optical isomers. Siberian chemical Magazine 1991 (5) Vorsina I.A., Grigoreva T.F., Barinova A.P., Lyakhov N.Z. Mecanochemical interaction of silicon dioxide with organic acids. Chemistry for sustainable development Magazine 2011(1) Grigoreva T.F., Vorsina I.A., Barinova A.P., Boldyrev V.V. Solid-state interaction of kaolinit and Acids during joint mechanical activation. Journal of Materials Synthesis and Processing 1996 (5) Vorsina I.A., Grigoreva T.F., Udalova T.A., Ovchinnicov E.V., Struk V.A., Lyakhov N.Z. Interaction of components in the system polymer + layered silicate during their joint mechanical activation. 3 ed Int Sience Techn Conf Promyshlen. Regiona: problems and perspective innovation progress. Grodno, Woodstone Publishing Yariv S., Cross H. Organo Clay Complexes and Interaction. Marcel Dekker. Inc. New York. Basel